Application is damaged and cannot be opened

If you download an unsigned application and try to open it on MacOS, you can see an error like the following:

"application" is damaged and can't be opened. You should move it to the Trash.
Firefox downloaded this file today at XX:XX.

The application is not actually damaged; it has been quarantined. To fix this issue, run the following command in a terminal:

xattr -dr com.apple.quarantine "application.app"